This invention relates to heat exchangers and more particularly to automotive heat exchangers and radiators and to a method of making the same.
In heat exchangers such as automotive radiators, which consist of top and bottom headers with tubes attached to them and fins attached to the tubes, there is often a failure of the bond between the tubes and headers before there is a failure of the material from which the headers and tubes are made. This is usually a result of high tensile and shear stresses created from thermal expansions and contractions coupled with operational vibrations which cause the bonding material affixing the tubes to the headers to crack and fail.
A contributing factor to this failure is that most tubes in such heat exchangers are oval shaped and are joined to the headers by inserting the ends of the oval shaped tubes into oval shaped collared openings in the walls of the headers. These oval shaped tubes and the oval shaped openings do not allow for a particularly tight fit, and make it difficult to obtain a good weld. They also contribute to bonding material failure because of uneven stress distribution.
Another contributing factor to the failure of the bonding material is the corrosion of the same due to exposure to engine coolants.
In the prior art there are taught methods of forming flanged or collared openings such as in prior U.S. Pat. No. 4,373,369.